Wandering by elderly with dementia, and stumbling/falling accidents around beds have recently become societal problems, and there is a need to address these problems. By using bed load information to monitor the in-bed movement of elderly and new postoperative patients and other users who are in bed for long periods of time, it may be possible to more rapidly respond when abnormal circumstances occur.
As an example of a technique for using bed load information to determine the state of a user, Patent Citation 1 discloses a technique for determining the in-bed or out-of-bed state of a user through use of bed load information. However, the technique disclosed in Patent Citation 1 is not designed to monitor the movement on the bed of a user who is continuously in bed for a long period of time.
As an example of a technique for monitoring the movement of a user on a bed, Non-patent Citation 1 discloses a technique in which a small acceleration sensor is mounted to the wrist of the user to measure movement of the user at each specific period of time, and the sleeping or waking state of the user is determined. However, this technique requires that a sensor be mounted to the body of the bed user, and is therefore unsuitable as a technique for elderly patients with dementia, new postoperative patients, and the like.
In order to overcome the problems of the conventional techniques described above, Patent Citations 2 through 5 and Non-patent Citation 2 disclose a technique for calculating a center of gravity from load information of four points on a bed and using the center-of-gravity information to monitor the movement of a user in the bed.